<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<style type="text/css">
			.box {
				width: 200px;
				height: 200px;
				border: 1px solid red;

				display: grid;
			}

			.children-box {
				background: yellow;
				align-self: center;
				justify-self: center;
			}
		</style>

	</head>
	<body>
		<div id="app">
			<div class="box">
				<div class="children-box">111111</div>
			</div>
		</div>
	</body>
</html>
